The Foreign Institutional Investors (FIIs) were net buyers to the tune of Rs 870.89 crore in the futures & option segment on Monday.According to data released by the NSE, FIIs were net buyers of index futures to the tune of Rs 805.86 crore and they bought index options worth Rs 30.57 crore. They were net buyers of stock futures to the tune of Rs 40.62 crore while they sold stock options worth Rs 6.16 crore.As per data available on the Sebi website - FIIs were net buyers of stocks worth Rs 1,093.80 crore in the cash market on Friday. Mutual funds were net sellers of shares worth Rs 40.77 crore on the same day.